This invention relates generally to gas turbine engines and, more particularly, to thrust control features of an aircraft engine of the VTOL type.
For many years the so-called "fixed-wing" aircraft, wherein horizontal flight was efficiently obtained but the vertical movement in takeoff and landing was obtained only by the use of long runways and/or catapults, was the only type available. With the advent of the helicopter, the vertical takeoff and landing eliminated those difficult problems but the aircraft was then inefficient in horizontal flight. The so-called VTOL (vertical takeoff and landing) embodies a concept which incorporates the advantages of both the fixed-wing aircraft and helicopter to enable both vertical takeoff and landing and efficient horizontal flight.
The flexibility of the VTOL aircraft is generally obtained by the use of gas turbine engines to develop thrust which is, in turn, directed to either the vertically down or horizontally rearward directions. One approach is to use separate engines for lift and cruise, but of course the inefficiencies are substantial. Another approach is to use a plurality of gas turbine engines which are adaptable to varying their thrust forces from the vertical to the horizontal direction by way of appropriate thrust deflecting means. In order to maintain stability of the aircraft this approach necessarily requires at least three gas turbine engines, one in each wing and one in the nose of the aircraft.
The most common approach to VTOL aircraft is the use of a pair of gas turbine engines which drive a plurality of remote lift/cruise fans which are operated in the lift mode only during takeoff and landing and in the cruise mode only during horizontal flight. Drive connection between the gas turbine engines and the fans is made by either drive shafts or by tip turbine apparatus. Again, with this approach, it is recognized that at least three such lift/cruise fans are required in order to maintain the aircraft in a stable position. The fans are generally located one in each wing and one in the nose section of the aircraft. The engines located on the wings may be adaptable to direct the thrust either in the downward or the rearward direction to accommodate the respective lift and cruise conditions of operation. But the remote fan located in the nose section of the aircraft is used only for lift, with the forward position thereof accommodating pitch control of the aircraft by appropriate modulation of thrust. In other words, in order to provide pitch control for the aircraft it is necessary to have at least a pair of axially spaced engines, or remote fans with the relative thrust being adjustable in order to maintain the desired attitude of the aircraft. Since the forward or nose engine/remote fan can only be used for lift purposes, such an arrangement becomes inefficient during cruise operation.
Another problem associated with present VTOL engines is the fact that the large fans required for the increased thrust levels are necessarily tip speed limited and, thus, the shaft speeds are accordingly limited. This, in turn, makes it difficult to obtain an efficient match-up between the fan and turbine designs.
It is therefore an object of the present invention to provide a single engine which can be used to produce thrust for both lift and cruise conditions of a VTOL aircraft.
Another object of the present invention is the provision in a VTOL aircraft for eliminating the use of fans which can be used for lift purposes only.
Yet another object of the present invention is the provision in a VTOL aircraft for the elimination of a remote fan in the nose section of the aircraft.
Still another object of the present invention is the provision in a VTOL aircraft for providing pitch control with the use of a single engine.
Still another object of the present invention is the provision in a VTOL aircraft for an engine which is relatively light in weight and which operates to provide thrust in both the lift and cruise conditions of operation.
Still another object is the efficient coupling of a high RPM, lightweight turbine to a high airflow, high shaft speed fan device.
These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.